Results 1 to 8 of 8
  1. #1
    Join Date
    Oct 2001
    Posts
    161

    if my database is small enough to fit in memory, do i need to bother with scsi?

    i run a php/mysql driven site and my database is small enough that it fits in the memory of the system. does this mean, scsi would not benefit me much?

  2. #2
    Join Date
    Jun 2004
    Location
    Northwest Colorado
    Posts
    4,630
    (I'm going to pretend he's asking if he needs RAID, not SCSI. )

    You still need RAID. When the machine is rebooted, what happens to that database held in memory? It's written to disk before shutdown. Let's say the HD fails upon restart. Where's your data now?

    Ideally, on the rest of the RAID array, so you can reconstruct. What if you only have a single HD? Better have a current backup. When you backed up that database, the data wasn't read from memory, it was read from disk. If the HD fails and corrupts data, it's the corrupted data from the disk that's backed up, not the correct data in memory.

    There's always a benefit to using a RAID array.
    Eric J. Bowman, principal
    Bison Systems Corporation coming soon: a new sig!
    I'm just a poor, unfrozen caveman Webmaster. Your new 'standards' frighten, and confuse me...

  3. #3
    Join Date
    Oct 2001
    Posts
    161
    i backup the data seperately so i don't need raid. i do need high performance and many say scsi is better for database servers.

  4. #4
    Technically speaking, if you have a very active website which is database intensively, it would inevitably means that it would access the harddisk quite often and a SCSI because of its built-in disk controller, it would reduce the load on the server's CPU. This means that the CPU can be free to handle other activities.

    However, that is only useful when your activity is very high. An IDE would handle most of the requirement. If you don't want SCSI then you don't need to. The only thing is that there may be a couple of seconds slowdown during heavy activities.

    Like you say if you load the database to memory then there would in theory not be a need for a fast harddisk. However as all database intensive sites, it would require a fast CPU to handle the server. It all depends on your load.

  5. #5
    Join Date
    Jan 2003
    Posts
    1,715
    Originally posted by BigBison
    When you backed up that database, the data wasn't read from memory, it was read from disk. If the HD fails and corrupts data, it's the corrupted data from the disk that's backed up, not the correct data in memory.
    How do you figure that? A single-host filesystem has no reason to invalidate disk cache. Any data that's in disk cache (per this query's definition, that would be all of it) should be read from disk cache, or you have a very broken OS. I suppose you could raw-read the device to bypass cache, although that opens a pretty massive can of worms even without hardware failure.

    Write activity still must pushed to disk at some point. If you have a significant update/insert load, disk IO could still be a bottleneck. Generally, if you sustain more than 500k/sec of IO, I recommend SCSI. Otherwise, that money is better spent elsewhere.
    Game Servers are the next hot market!
    Slim margins, heavy support, fickle customers, and moronic suppliers!
    Start your own today!

  6. #6
    Join Date
    Jun 2004
    Location
    Northwest Colorado
    Posts
    4,630
    Originally posted by hiryuu
    Any data that's in disk cache...
    I thought the data was held in the database's memory, not the OS's disk cache? In which case corrupt data could be backed up from disk yet not reflected in a query. But what do I know? I misunderstood the OP in the first place and the intricacies of DB operation is about my weakest point.

  7. #7
    Join Date
    Feb 2001
    Location
    Solar Star system
    Posts
    183
    If u can fit database in memory then your DISK speed will not be important.

    Let say your databse is 10 MB in size.

    Only time when your hard drive will be accessed is for system files from OS or for static pages if u host on same server.

    Also u should think about this - how much often u will write down (dump) databse back to hard drive.

    Cause if your server crash or whatver (reboot etc) - u will lose all your data.

    We have solution for some of our clients that database is writen down to hard drive every 5 minutes from memory.

    So in worst case u will lost 5 minutes of data. In same case we have set that each time there is some "write" in database we are doin dump on harddrive to prevent any loss of data.

    Database from memory really works great, your website can really work fast this way, but u need to take care of your data in case something bad happen.

    Bottom line - if u doin what u doin - u dont need SCSI - but cant hurt

    N.

  8. #8
    Join Date
    Oct 2003
    Location
    Hanoi
    Posts
    4,306
    we have compared 2 servers: P4 3GHz with IDE HDD, and P3 733 with SCSI HDD. The server load in P4 is around 0.3. And in P3 is around 0.2. Customers in P3 box are much happier than other.

    I am a big fan of SCSI

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •